An image processing method for detecting a specific object pattern based on an image can be utilized in detecting a face of a person. Accordingly, the image processing method can be used in various occasions and technological fields, such as a teleconference, a man-machine interface, a security system, and a monitoring system that tracks a face of a person.
To detect a face of a person in an image, a method discussed in Yang et al, “Detecting Faces in Images: A Survey”, IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE, VOL. 24, No. 1, JANUARY 2002 can be used, for example. This method detects a face of a person based on a few remarkable characteristics (e.g., the eyes, the mouse, the nose of a person's face) and a geometrical positional relationship among the characteristics.
In addition, Yang et al, “Detecting Faces in Images: A Survey”, IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE, VOL. 24, No. 1, JANUARY 2002 discusses a method for detecting a face of a person based on a symmetrical characteristic of a person's face and a characteristic of a color of a face of a person and by utilizing a template matching method and a neural networking method.
In recent years, a method is desired capable of identifying and recognizing a specific person based on a detected face of a person in addition to simply detecting a person's face. More specifically, if a specific person can be identified and recognized from an image of a plurality of persons have been captured, an application for recognizing a face of a person captured in the image by using a camera and configured to execute appropriate exposure and focus control according to the recognized face can execute control appropriate for the specific person.
However, recognition of a person's face and a specific person's face cannot be easily implemented for the present. More specifically, Japanese Patent Application Laid-Open No. 2007-115109 discusses a method that recognizes a person's face based on a characteristic of the color of the skin of the person, acquires a focused area of the recognized face, and recognizes the face of a specific person based on a location of the acquired focused area which is used as a characteristic amount.
This method separately executes recognition of a person's face and recognition of a specific person's face. If processing for recognizing the specific person's face in an image is simply used in combination, it becomes necessary to calculate a characteristic amount and execute face recognition in each processing. Accordingly, in this case, it is necessary to execute complicated processing.
The above described problem generally arises not only in executing the face recognition and the recognition of the specific person's face in combination but also in executing recognition of an object in an upper order and another object in a lower order in combination.
In other words, it is desired that a face recognition application is capable of recognizing a lower order object, such as a specific person's face, after recognizing an upper order object, such as a face of a person.
Further, for an application that searches for an image of an animal by recognizing an image of an animal from among a vast amount of images, it is desired to search for an image of a dog, which belongs to a category lower than the category of the animal image. In addition, for a car navigation application that recognizes and highlights a traffic sign and a signboard captured in a video of a scene of a running car, it is desired to identify and highlight a specific signboard.